How does Brutus' tragic flaw of idealism contribute to his downfall?

Brutus' tragic flaw of idealism contributes to his downfall because he was gullible enough to be convinced by Cassius and Antony that they were going to murder Julius Caesar for Rome's development and goodwill. He was blinded by that idealism and believed that these were their true intentions for inviting him in the murder, thus, making him involved greatly and made him feel guilty - leading him to suicide.